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  2. Triangular number - Wikipedia

    en.wikipedia.org/wiki/Triangular_number

    The final digit of a triangular number is 0, 1, 3, 5, 6, or 8, and thus such numbers never end in 2, 4, 7, or 9. A final 3 must be preceded by a 0 or 5; a final 8 must be preceded by a 2 or 7. In base 10, the digital root of a nonzero triangular number is always 1, 3, 6, or 9. Hence, every triangular number is either divisible by three or has a ...

  3. Lunar arithmetic - Wikipedia

    en.wikipedia.org/wiki/Lunar_arithmetic

    The lunar addition and multiplication operations satisfy the commutative and associative laws. The lunar multiplication distributes over the lunar addition. The digit 0 is the identity under lunar addition. No non-zero number has an inverse under lunar addition. The digit 9 is the identity under lunar multiplication.

  4. Doubly triangular number - Wikipedia

    en.wikipedia.org/wiki/Doubly_triangular_number

    In mathematics, the doubly triangular numbers are the numbers that appear within the sequence of triangular numbers, in positions that are also triangular numbers. That is, if T n = n ( n + 1 ) / 2 {\displaystyle T_{n}=n(n+1)/2} denotes the n {\displaystyle n} th triangular number, then the doubly triangular numbers are the numbers of the form ...

  5. 1 + 2 + 3 + 4 + ⋯ - ⋯ - Wikipedia

    en.wikipedia.org/wiki/1_%2B_2_%2B_3_%2B_4_%2B_%E...

    The nth partial sum of the series is the triangular number ... (2k − 1)th derivative of f and B 2k is the (2k)th Bernoulli number: B 2 = ⁠ 1 / 6 ...

  6. Squared triangular number - Wikipedia

    en.wikipedia.org/wiki/Squared_triangular_number

    A square whose side length is a triangular number can be partitioned into squares and half-squares whose areas add to cubes. From Gulley (2010).The n th coloured region shows n squares of dimension n by n (the rectangle is 1 evenly divided square), hence the area of the n th region is n times n × n.

  7. Löschian number - Wikipedia

    en.wikipedia.org/wiki/Löschian_number

    In number theory, the numbers of the form x 2 + xy + y 2 for integer x, y are called the Löschian numbers (or Loeschian numbers). These numbers are named after August Lösch. They are the norms of the Eisenstein integers. They are a set of whole numbers, including zero, and having prime factorization in which all primes congruent to 2 mod 3 ...

  8. APL syntax and symbols - Wikipedia

    en.wikipedia.org/wiki/APL_syntax_and_symbols

    Take Pascal's triangle, which is a triangular array of numbers in which those at the ends of the rows are 1 and each of the other numbers is the sum of the nearest two numbers in the row just above it (the apex, 1, being at the top). The following is an APL one-liner function to visually depict Pascal's triangle:

  9. 6 - Wikipedia

    en.wikipedia.org/wiki/6

    Only five such numbers are known to exist. [3] 6 is the largest of the four all-Harshad numbers. [4] 6 is the 2nd superior highly composite number, [5] the 2nd colossally abundant number, [6] the 3rd triangular number, [7] the 4th highly composite number, [8] a pronic number, [9] a congruent number, [10] a harmonic divisor number, [11] and a ...